STRUCTURAL AND DIMENSIONAL STABILITIES OF TIN-BISMUTH FUSIBLE CORES

Eutectic tin-bismuth alloys, used as fusible cores for high polymer in jection moulding, were studied in order to identify structural and dim ensional modifications during ageing at temperatures ranging from 4 to 110 degrees C. Optical and scanning electron microscopies together wi th X-ray diffraction were used to observe the coarsening of the eutect ic structure and to plot an isothermal transformation diagram. Thermal cycles around the eutectic temperature promoted the dissociation of t he eutectic structure into light tin dendrites at the top of the ingot s and heavy bismuth crystals at the bottom. Differential scanning calo rimetry and thermomechanical analysis were performed to observe possib le phase transformations.